System and method of maximizing performance of a solid-state closed loop well heat exchanger

ABSTRACT

A heat exchanger transfers heat from solid state heat conducting material to a fluid in a closed loop system. A heat harnessing component includes a closed-loop solid state heat extraction system having a heat exchanging element positioned within a heat nest in a well designed to optimize the transfer of heat from heat conductive material to a closed loop fluid flow. A piping system conveys contents heated by the heat exchanging element to a surface of the well.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of United StatesNon-Provisional patent application Ser. No. 12/456,434 filed on Jun. 15,2009. This application also claims priority to 1) U.S. ProvisionalApplication No. 61/137,956, filed on Aug. 5, 2008; 2) U.S. ProvisionalApplication No. 61/137,974, filed on Aug. 5, 2008; 3) U.S. ProvisionalApplication No. 61/137,955, filed on Aug. 5, 2008; and 4) U.S.Provisional Application No. 61/137,975, filed on Aug. 5, 2008, thecontents of all of which are hereby incorporated in their entirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISK APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of convertinggeothermal energy into electricity. More specifically, the presentinvention relates to capturing geothermal heat from deep within adrilled well and bringing this geothermal heat to the Earth's surface togenerate electricity in an environmentally friendly process.

Wells that have been drilled for oil and gas exploration that are eitherdepleted, or have never produced oil or gas, usually remain abandonedand/or unused and may eventually be filled. Such wells were created at alarge cost and create an environmental issue when no longer needed fortheir initial use.

Wells may also be drilled specifically to produce heat. While there areknown geothermal heat/electrical methods and systems for using thegeothermal heat/energy from deep within a well (in order to produce aheated fluid (liquid or gas) and generate electricity therefrom), thesemethods have significant environmental drawbacks and are usuallyinefficient in oil and gas wells due to the depth of such wells.

More specifically, geothermal heat pump (GHP) systems and enhancedgeothermal systems (EGS) are well known systems in the prior art forrecovering energy from the Earth. In GHP systems, geothermal heat fromthe Earth is used to heat a fluid, such as water, which is then used forheating and cooling. The fluid, usually water, is actually heated to apoint where it is converted into steam in a process called flash steamconversion, which is then used to generate electricity. These systemsuse existing or man made water reservoirs to carry the heat from deepwells to the surface. The water used for these systems is extremelyharmful to the environment, as it is full of minerals, is caustic andcan pollute water aquifers. Such deep-well implementations require thata brine reservoir exists or that a reservoir is built by injecting hugequantities of water into an injection well, effectively requiring theuse of at least two wells. Both methods require that polluted dirtywater is brought to the surface. In the case of EGS systems, waterinjected into a well permeates the Earth as it travels over rock andother material under the Earth's surface, becoming polluted, caustic,and dangerous.

A water-based system for generating heat from a well presentssignificant and specific issues. For example, extremely large quantitiesof water are often injected into a well. This water is heated and flowsaround the inside of the well to become heated and is then extractedfrom the well to generate electricity. This water becomes polluted withminerals and other harmful substances, often is very caustic, and causesproblems such as seismic instability and disturbance of naturalhydrothermal manifestations. Additionally, there is a high potential forpollution of surrounding aquifers. This polluted water causes additionalproblems, such as depositing minerals and severely scaling pipes.

Geothermal energy is present everywhere beneath the Earth's surface. Ingeneral, the temperature of the Earth increases with increasing depth,from 400°-1800° F. at the base of the Earth's crust to an estimatedtemperature of 6300°-8100° F. at the center of the Earth. However, inorder to be useful as a source of energy, it must be accessible todrilled wells. This increases the cost of drilling associated withgeothermal systems, and the cost increases with increasing depth.

In a conventional geothermal system, such as for example and enhancedgeothermal system (EGS), water or a fluid (a liquid or gas), is pumpedinto a well using a pump and piping system. The water then travels overhot rock to a production well and the hot, dirty water or fluid istransferred to the surface to generate electricity.

As mentioned earlier herein, the fluid (water) may actually be heated tothe point where it is converted into gas/steam. The heated fluid orgas/steam then travels to the surface up and out of the well. When itreaches the surface, the heated water and/or the gas/steam is used topower a thermal engine (electric turbine and generator) which convertsthe thermal energy from the heated water or gas/steam into electricity.

This type of conventional geothermal system is highly inefficient invery deep wells for several of reasons. First, in order to generate aheated fluid required to efficiently operate several thermal engines(electric turbines and generators), the fluid must be heated to degreesof anywhere between 190° F. and 1000° F. Therefore the fluid must obtainheat from the surrounding hot rock. As it picks up heat it also picks upminerals, salt, and acidity, causing it to very caustic. In order toreach such desired temperatures in areas that lack a shallow-depthgeothermal heat source (i.e. in order to heat the fluid to this desiredtemperature), the well used must be very deep. In this type of prior artsystem, the geologies that can be used because of the need for largequantities of water are very limited.

The deeper the well, the more challenging it is to implement awater-based system. Moreover, as the well becomes deeper the gas orfluid must travel further to reach the surface, allowing more heat todissipate. Therefore, using conventional geothermalelectricity-generating systems can be highly inefficient because longlengths between the bottom of a well and the surface results in the lossof heat more quickly. This heat loss impacts the efficacy and economicsof generating electricity from these types of systems. Even more wateris required in such deep wells, making geothermal electricity-generatingsystems challenging in deep wells.

Accordingly, prior art geothermal systems include a pump, a pipingsystem buried in the ground, an above ground heat transfer device andtremendous quantities of water that circulates through the Earth to pickup heat from the Earth's hot rock. The ground is used as a heat sourceto heat the circulating water. An important factor in determining thefeasibility of such a prior art geothermal system is the depth ofwellbore, which affects the drilling costs, the cost of the pipe and thesize of the pump. If the wellbore has to be drilled to too great adepth, a water-based geothermal system may not be a practicalalternative energy source. Furthermore, these water-based systems oftenfail due to a lack of permeability of hot rock within the Earth, aswater injected into the well never reaches the production well thatretrieves the water.

BRIEF SUMMARY OF THE INVENTION

Wells that have been drilled for oil and gas exploration that are eitherdepleted, or have never produced oil or gas, can now be used to generateelectricity. Wells can also be drilled specifically for the purpose ofgenerating electricity. The only requirement is that the wells are deepenough to generate heat from the bottom of the well. The invention is aprocess for maximizing the performance of a heat exchanger that residesat the heat zone of a geothermic system in a well. The heat exchangingmechanism is a combination of a fluid heat exchanging element 3, heatconductive material and grout 6. The fluid heat exchanging mechanismmaximizes the heat transfer from the bottom of the well to the surface.The invention uses a heat exchanger that has a fluid component and asold state heat flow component where the solid state heat flow componenttransfers heat to the fluid.

There are pipe(s) carrying the heat conducting fluid into the fluid heatexchanging mechanism (fluid heat exchanging element plus heat conductivematerial and grout) at the bottom of the well from the surface andpipe(s) carrying the fluid, after being heated, back to the surface.

The heat exchanging mechanism needs to be able to enable the maximumamount of fluid flow while also maximizing the heat exchange to thefluid.

The pipe(s) need to minimize heat loss while transporting the fluid. Thevolume of fluid that flows through the fluid heat exchanging elementneeds to be as high a multiple as possible compared to the fluid flow ofthe pipe(s).

The rate of flow of the fluid in the fluid heat exchanging element willtherefore be decreased by the volume differences between the pipe andthe heat exchanger element. By slowing down the fluid flow in the fluidheat exchanging element you increase the time the fluid is exposed tothe heat conductive material and grout in the heat zone and increase theheat that is transferred to the fluid. This allows the heat conductivematerial and grout part of the heat exchanging mechanism time to conductand transfer the heat to the fluid. A standard heat exchanger transfersthe heat from one fluid to another. The following embodiments transfer asolid state heat flow to a fluid.

Other embodiments, features and advantages of the present invention willbecome more apparent from the following description of the embodiments,taken together with the accompanying several views of the drawings,which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a conceptual view of a system according to one embodiment ofthe present invention showing a fluid heat exchanging element having amuch larger diameter than the feeder pipes;

FIG. 2 is a conceptual view of a system according to another embodimentof the present invention showing a double helix design of the fluid heatexchanging element;

FIG. 3 is a conceptual view of a system according to another embodimentof the present invention showing the fluid heat exchanging element as acollection of smaller heat exchanger pipes where the sum of the volumecapacity of the pipes is greater than the volume capacity of the feederpipes;

FIG. 4 is a conceptual view of a system according to another embodimentof the present invention showing the fluid heat exchanging element builtin modules having a total length that is the sum of the modules; and

FIG. 5 is a cross-sectional, conceptual view of pipes according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the present invention reference is madeto the accompanying drawings which form a part thereof, and in which isshown, by way of illustration, exemplary embodiments illustrating theprinciples of the present invention and how it may be practiced. It isto be understood that other embodiments may be utilized to practice thepresent invention and structural and functional changes may be madethereto without departing from the scope of the present invention.

FIG. 1 illustrates a first preferred embodiment for the fluid heatexchanging element 3 where the element has a much larger diameter thenthe feeder pipes 2. The larger diameter slows the rate of flow of thefluid while it flows through the heat nest 10 portion of the system. Theslower flow characteristics allow the fluid a longer time to pick up theheat from the heat conductive material and grout 6. The fluid travelsdown and up of the fluid heat exchanging element picking up heat;

FIG. 2 illustrates a second preferred embodiment for the fluid heatexchanging element 3 where the element is a double helix design. Thedouble helix pipes have an equal or larger diameter than the feederpipes and the twisted nature of the pipes increase the length of thetravel path within the heat nest 10. The increased travel path (and thelager diameter if present) increase the time the fluid spends within theheat nest 10 portion of the system and the twisted pipe arrangementincreases the heat transfer surface area increasing the transfercapability. The increased time allows the fluid a longer time to pick upthe heat from the heat conductive material and grout 6 and the increasedsurface area increase the transfer capacity. The fluid travels down andup of the fluid heat exchanging element picking up heat;

FIG. 3 illustrates a third preferred embodiment for the fluid heatexchanging element 3 where the element is a collection of smaller heatexchanger pipes 4 where the sum of the volume capacity of the pipes isgreater than the volume capacity of the feeder pipes 2. The increasedvolume of the heat exchanger pipes slows the fluid flow and theincreased surface area of the pipes (versus a single pipe) increases theheat transfer capability. The smaller diameter of the pipes allows moreof the fluid to be exposed to the heat thereby increasing the capabilityof the transfer of heat. The larger volume of the heat exchanger pipesincrease the time the fluid spends within the heat nest 10 portion ofthe system and the increased surface area of he pipe surface increasesand the smaller diameters increases the heat transfer capability. Theincreased time allows the fluid a longer time to pick up the heat fromthe heat conductive material and grout 6 and the increased surface areaand smaller diameters improves the transfer capability per linear foot.The fluid travels down and up of the fluid heat exchanging elementpicking up heat;

FIG. 4 illustrates an embodiment of the fluid heat exchanging elementwhere the element can be built in modules and the total length is thesum of the attached modules. The last module (FIG. 3) located at thebottom of the well has the downward flowing feeder pipe attached to theupward flowing feeder pipe creating a U-connection. As an example if thefluid heat exchanging element needed to be 500 feet long we can build itby connecting twenty five (25) twenty foot (20) modules. The moduleimplementation can be accomplished regardless of the design of the heatexchanging element.

Each of the preferred embodiments is designed to maximize the exchangeof heat from a solid state heat flow environment (heat conductivematerial and grout 6) to a fluid environment. This is accomplished bydesigning a fluid heat exchanging element that accomplishes one or moreof the following functions:1. Increases the fluid volume capacity of the heat exchanging elementcompared to the volume capacity of the feeder pipes. This increases thetime the fluid spends in the heat nest thereby increasing the amount ofheat that can be transferred;2. Increase the surface area of the fluid heat exchanging elementthereby increasing the linear capacity to exchange heat;3. Modularize the design so the fluid heat exchanging element can be aslong as required;4. Decrease the diameter of the heat exchanging pipes allowing more ofthe fluid to touch the heat exchanging surface of the pipe;5. Use heat conductive material and gout instead of a fluid to conductheat from the hot rock to the heat exchanging element;6. Use flexible connectors to attached the fluid heat exchanging modulestogether. These flexible connectors will provide a level of protectionagainst earth movement, tremors and earth quakes;7. The heat exchanger must fit into the bore hole of a well.Referring now to FIG. 1, there is shown a preferred embodiment for theheat exchanging element 3 utilized in the present invention. Heatexchanging elements are devices built for efficient heat transfer whichtypically transfer heat from one fluid to another. They are widely usedin many engineering processes. Some examples include intercoolers,pre-heaters, boilers and condensers in power plants. By applying thefirst law of thermodynamics to a heat exchanger working at steady-statecondition, we obtain:

mi hi=0

where,

mi=mass flow of the i-th fluid

hi=change of specific enthalpy of the i-th fluid

In a preferred embodiment, the heat exchanging element utilized in thepresent invention is a high-temperature heat exchanger (“HTHE”)comprised of a recuperative type “cross flow” heat exchanger, in which afluid exchanges heat with a solid state heat flow on either side of adividing wall. Alternatively, the heat exchange element may be comprisedof an HTHE which utilizes a regenerative and/or evaporative design. Theembodiments of the invention replace one of the fluids with a solidstate heat flow.

In a preferred embodiment FIG. 3, the heat exchanger will have aplurality of smaller capillaries (heat exchanger pipes 5). The fluidenters the heat exchanger from the downward flowing feeder pipe(s) 2,where it is then dispersed, flowing through each of the plurality ofsmaller capillaries. Preferably the capillaries are thinner (having asmaller diameter than the downward flowing pipe(s), thereby allowing thefluid to heat more quickly as it passes through thecapillaries—increasing the overall efficacy of the heat exchanger. In apreferred embodiment, the combined flow of the capillaries of the heatexchanging element must be able to accommodate an equal or greater flowthen the downward and upward flow pipe(s). This greater flow increasesthe time the fluid spends in the heat exchanger.

In a preferred embodiment, the heat exchanging element may be comprisedfrom a titanium clad tube sheet, wherein the tube sheet may be formedfrom a high temperature nickel based alloy or ferritic steel. In thisway, the heat exchanger is able to operate efficiently under hightemperature/pressure conditions. Moreover, the thickness of thetitantium may vary in accordance with specific temperature and/orpressure conditions under which the heat exchange element operates.

It is understood that there are other types of heat exchanging elementsknown the art which may also be used in the present invention such asparallel heat exchangers and/or reverse flow heat exchangers. Inalternative embodiments, any of these types of exchangers may beutilized. A primary consideration in designing the heat exchangingelement will be to ensure its efficient operation under hightemperature/pressure conditions. Further, any such heat exchangerutilized in the present invention must be sized to fit within the borehole of the well.

Still referring to FIG. 1, the upward flowing feeder pipe(s) 2 of thepiping system are preferably coupled to the heat exchanging element 3 onan opposite side of the element. The upward flowing pipe(s) 2 draw theheated fluid from the heat exchanging element 3 and bring the heatedfluid upward from the “heat point” in the well to the top surface.

In a preferred embodiment, the fluid that is used should be optimized tocarry heat. An example of such a fluid is the antifreeze used inautomobiles. Gas or water can also be used as a fluid. Further, thefluid cannot and should not have any corrosive properties and the pipingmaterial needs to be resistant to the fluid. Moreover, the fluid will bepressurized within the piping system so the system should be able towithstand the pressure generated by the depth of the well and thepumping mechanism, as the fluid is pumped through the system.

Referring still to FIG. 1, once the piping and heat exchanging elementare fully installed in the well, the well is completely filled with aheat conductive material and grout 6. The heat conductive material andgrout 6 must have heat conductive properties and preferably will bondand solidify within the well. In the preferred embodiment wherein thewell is insulated, the heat exchanging element will be lowered into thewell and then the heat conductive material and the grout will beinserted into the well before the insulation.

It is to be understood that other embodiments may be utilized andstructural and functional changes me be made without departing from thescope of the present invention. The foregoing descriptions of theembodiments of the invention have been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Accordingly, manymodifications and variations are possible in light of the aboveteachings. It is therefore intended that the scope of the invention notbe limited by this detailed description.

1. A heat exchanger positioned at the bottom of a well that transfersheat from solid state heat conducting material to a fluid in a closedloop system comprising: a heat harnessing component having a closed-loopsolid state heat extraction system, the closed-loop solid state heatextraction system including a heat exchanging element positioned withina heat nest in a well designed to optimize the transfer of heat fromheat conductive material to a closed loop fluid flow; and a pipingcomponent including a set of downward-flowing pipes and a set ofupward-flowing pipes, the upward-flowing pipes conveying contents of thepiping component heated by the heat exchanging element to a surface ofthe well.
 2. The system of claim 1, wherein the downward-flowing pipescouple to a first side of the heat exchanging element.
 3. The system ofclaim 1, wherein the upward-flowing pipes couple to a second side of theheat exchanging element.
 4. The system of claim 1, wherein the heatexchanging element is a pipe that has a larger diameter than thedownward and upward piping components.
 5. The system of claim 1, whereinthe heat exchanging element comprises a double helix shape where thediameter of the pipe in the double helix is equal to or greater than thedownward and upward pipe components in which the piping system withinthe heat exchanging element comprises at least one twisted pipe toincrease the distance and slow the of the fluid flowing through thepiping system of the heat exchanging element.
 6. The system of claim 1,wherein the heat exchanging element includes a plurality of capillaries.7. The system of claim 6, wherein the contents of the downward-flowingpipes are dispersed through the plurality of capillaries after enteringthe heat exchanging element.
 8. The system of claim 7, wherein eachcapillary in the plurality of capillaries has a diameter smaller than adiameter of the downward-flowing pipes, thereby allowing the contents ofthe piping system to heat quickly as the contents pass through theplurality of capillaries.
 9. The system of claim 8, wherein the sum ofthe volume of the capillaries attached to each of the downward andupward pipe components is greater than the volume of the pipe componentsthereby allowing the fluid to spend more time in the heat exchangingelement.
 10. The system wherein the heat exchanging element is built inmodules that attach to one another with connecting pipes to form a heatexchanger of variable length. The heat exchanger element module at thebottom of the string of modules connects the downward flowing pipe tothe upward flowing pipe creating a closed loop.